Rare Skills are a system implemented in Lineage 2 Revolution.
Official Summary
Lineage 2 Revolution is implementing a rare skill system. With this system, experienced adventurers who have gone through a lot of training can use powerful skills regardless of their race or class. Unlike ordinary skills which can only e learned by attaining the appropriate level, rare skills can be learnt by making a Rare Forgotten Scroll after obtaining a Skill Page.
There are various types of Rare Skills. There is a wide range of uses for the skills regardless of what class uses it. There are also attractive skills that can inflict strong damage regardless of what class uses them. Why not challenge yourself and show your character strength by obtaining the rarest skill regardless of race, class, armor, or defense.